FIG. 1 shows a ducted fan gas turbine engine 10 comprising, in axial flow series: an air intake 12, a propulsive fan 14 having a plurality of fan blades 16, an intermediate pressure compressor 18, a high-pressure compressor 20, a combustor 22, a high-pressure turbine 24, an intermediate pressure turbine 26, a low-pressure turbine 28 and a core exhaust nozzle 30. A nacelle 32 generally surrounds the engine 10 and defines the intake 12, a bypass duct 34 and a bypass exhaust nozzle 36.
Air entering the intake 12 is accelerated by the fan 14 to produce a bypass flow and a core flow. The bypass flow travels down the bypass duct 34 and exits the bypass exhaust nozzle 36 to provide the majority of the propulsive thrust produced by the engine 10. The core flow enters in axial flow series the intermediate pressure compressor 18, high pressure compressor 20 and the combustor 22, where fuel is added to the compressed air and the mixture burnt. The hot combustion products expand through and drive the high, intermediate and low-pressure turbines 24, 26, 28 before being exhausted through the nozzle 30 to provide additional propulsive thrust. The high, intermediate and low-pressure turbines 24, 26, 28 respectively drive the high and intermediate pressure compressors 20, 18 and the fan 14 by interconnecting shafts 38, 40, 42.
It is known in modern gas turbine engines 10 to use a boroscope to inspect the interior of the engine 10 both after assembly and during servicing to detect the fitness of the engine 10. Thus, engines 10 are known to have inspection ports in various locations to allow boroscopes to be inserted. FIG. 2 shows such a port 210 for a compressor 18 which includes an outer casing wall 212 and an inner casing wall 214 which house annular arrays of compressor rotor blades 216 and stator vanes 218. The port 210 includes flanged apertures 220, 222 through the inner 214 and outer 212 walls and is shown in a closed configuration in which the apertures 220, 222 are sealed with a plug 224. In this known example, the plug 224 constitutes sealing members 226, 228 for the inner and outer wall apertures 220, 222 which are linked by a link rod 230. The plug 224 can be realisably secured within the port 210 in any suitable manner and configured to be removed from the exterior of the compressor 18 when boroscope access is required. As will be appreciated, once removed, a boroscope can be inserted as required.
Typically, the inspection ports 210 are located around the engine core so that, for example, each stage of the compressor 18 may have a circumferential distribution of inspection ports, as might the combustor or various turbine stages.
The present invention seeks to provide an improved way of inspecting the interior of an internal combustion engine.